1. Field of the Invention
The present invention relates generally to the packaging of semiconductor integrated circuit (IC) die and, in particular, to the packaging of semiconductor IC die in chip scale packages at the wafer level structure of the integrated circuit manufacturing process. In one of its aspects, the invention specifically relates to packaging individual semiconductor IC die at the wafer structure level in chip scale packages that are hermetically sealed against moisture and other environmental conditions.
2. Discussion of the Related Art
Chip Scale Packages (CSP) for semiconductor die currently embody some form of solder ball or bump to attach the die to the next higher assembly in the total package. In the simplest form of a CSP, the CSP is a flip-chip semiconductor die that has additional solder bumps to be connected to normal bond pads on, for example, a printed circuit board (PCB) substrate.
The most recent innovations in flip-chip technology involve the relocation of the solder ball/bump sites from the close pitch pads that are normally placed around the perimeter of the semiconductor die to an array located across the surface of the die. This is accomplished by creating new traces from the perimeter locations to the new array locations on top of a passivation layer. The passivation layer is typically a spun-on glass layer formed on the surface of the die; openings are formed in the glass to expose the bond pads or by adding an interposer connector, which is bonded to the existing pads and reroutes traces to the array.
A current interposer connector process reroutes connectors to the pads by extending them into the space between adjacent die as created on the semiconductor wafer, laminating a piece of glass to either side of the wafer and then through a complex series of mechanical cutting, metal deposition and etching operations, the connectors to the pads are extended to the surface of the glass. This produces an array on the top of the glass covering the die, which is in turn adhesively bonded to the passivation surface of the die. The advantage of this process and structure is that the glass provides a protective surface for the delicate surface of the passivated die and allows some degree of differential expansion between the die surface and the array of solder balls due to the non-rigid nature of the adhesive layer. The disadvantages are that the extension of the connectors to the pads on the wafer are difficult to implement and often prevent the process from being possible, the glass cutting operation is costly and requires special equipment, the process is implemented on a completed semiconductor wafer which is very sensitive and costly and any error causes the entire wafer to be scrapped, and two sheets of glass are always required.
Therefore, what is needed is a chip scale flip chip process that is easy to implement, uses one glass sheet and is inexpensive.